The present invention relates to a screwer test bench and in particular to a bench with a resisting torque simulation unit realized with a friction brake.
In the prior art screwer test benches are well known. Such benches simulate the resisting torque of a screw in tightening and at the same time measure the parameters of torque and angle developed by a screwer applied to the bench and signal deviations of said parameters from a predetermined characteristic curve.
In such benches correct simulation of resisting torque is the most critical part in order that the measurements made be truly representative of the operation of the screwer in normal use.
In accordance with a known system the bench comprises a cap to which is engaged the screwer being tested. A friction disk is thrust against the cap by means of a hydraulic cylinder to produce the braking force. Naturally as all the torque produced by the screwer is discharged onto the friction disk this disk must be locked against axial rotation. As the thrust cylinder cannot offer any resistance to rotation, the disk runs along purposeful guides which prevent its rotation so it can move only axially to draw near the cap to be braked.
The holder of this application has noted however that this simple structure involves some problems in the generation of the braking ramp and consequently in the accuracy of the measurements made with the bench.
Indeed, in benches made in this manner there have been found measurement oscillations in particular near the stop. These oscillations are due mainly to the braking system structure used.
Indeed, there is play even if small in the coupling between the disk and guides which is indispensable for allowing free axial running of the disk along the guides. It was found that this play during braking simulation generates oscillations of a cyclic nature which alter braking linearity.
The general purpose of the present invention is to remedy the above mentioned shortcomings by making available a screwer test bench free of measurement uncertainty problems caused by vibration and oscillations produced by the known braking systems described.
In view of this purpose it was sought to provide in accordance with the present invention a screwer test bench comprising a coupling connected to a braking unit and designed for coupling with the head of a screwer, and a sensor unit detecting mechanical magnitudes transmitted between the coupling and the braking unit and the braking unit comprising a friction brake with braking surfaces which upon operation of the brake are thrust upon command one against the other in a braking direction characterized in that the brake has a movable thrust member of said braking surfaces in said braking direction which is constrained against rotation around the brake axis by means of an inextensible wall with configuration deformable in said braking direction.